To obtain hydrocarbon fluids from an earth formation, a wellbore is drilled into an area of interest within a formation. The wellbore may then be “completed” by inserting casing in the wellbore and setting the casing using cement. Alternatively, the wellbore may remain uncased as an “open hole”), or it may be only partially cased. Regardless of the form of the wellbore, production tubing is run into the wellbore to convey production fluid (e.g., hydrocarbon fluid, which may also include water) to the surface.
Often, pressure within the wellbore is insufficient to cause the production fluid to naturally rise through the production tubing to the surface. In these cases, an artificial lift system can be used to carry the production fluid to the surface. One type of artificial lift system is a gas lift system, of which there are two primary: tubing-retrievable gas lift systems and wireline-retrievable gas lift systems. Each type of gas lift system uses several gas lift valves spaced along the production tubing. The gas lift valves allow gas to flow from the annulus into the production tubing so the gas can lift production fluid in the production tubing. Yet, the gas lift valves prevent fluid to flow from the production tubing into the annulus.
A typical wireline-retrievable gas lift system 10 is shown in FIG. 1. Operators inject compressed gas G into the annulus 22 between a production tubing string 20 and the casing 24 within a cased wellbore 26. A valve system 12 supplies the injection gas G from the surface and allows produced fluid to exit the gas lift system 10.
Side pocket mandrels 30 spaced along the production string 20 hold gas lift valves 40 within side pockets 32. As noted previously, the gas lift valves 40 are one-way valves that allow gas flow from the annulus 22 into the production string 20 and to prevent gas flow from the production string 20 into the annulus 22.
A production packer 14 located on the production string 20 forces the flow of production fluid P from a formation up through the production string 20 instead of up through the annulus 22. Additionally, the production packer 14 forces the gas flow from the annulus 22 into the production string 20 through the gas lift valves 40.
In operation, the production fluid P flows from the formation into the wellbore 26 through casing perforations 28 and then flows into the production tubing string 20. When it is desired to lift the production fluid P, compressed gas G is introduced into the annulus 22, and the gas G enters from the annulus 22 through ports 34 in the mandrel's side pockets 32. Disposed inside the side pockets 32, the gas lift valves 40 control the flow of injected gas I into the production string 20. As the injected gas I rises to the surface, it helps to lift the production fluid P up the production string 20 to the surface.
Gas lift valves 40 have been used for many years to inject compressed gas into oil and gas wells to assist in the production to the surface. The valves 40 use metal bellows to convert pressure into movement. Injected gas acts on the bellows to open the valve 40, and the gas passes through a valve mechanism into the tubing string. As differential pressure is reduced on the bellows, the valve 40 can close.
Two types of gas lift valves 40 use bellows. One type uses a non-gas charged, atmospheric bellows and requires a spring to close the valve mechanism. The other type of valve 40 uses an internal gas charge, usually nitrogen, in a volume dome to provide a closing force on the bellows. In both valve configurations, pressure differential on the bellows from injected high-pressure gas opens the valve mechanism. In the case of a valve having the non-gas charged bellows, the atmospheric bellows is subjected to high differential pressures when the valve 40 is installed in a well and can be exposed to high operating gas injection pressure. By contrast, a valve having the gas-charged bellows is subject to high internal bellows pressure during setting and prior to installation. Yet, once the gas-charged valve is installed, the differential pressure across the bellows is less than in the non-gas charged bellows during operation of the valve.
Prior art gas lift valves 40a-b having gas-charged bellows are shown in FIGS. 2A-2B. Each of the gas lift valves 40a-b has upper and lower seals 44a-b separating a valve port 46, which is in communication with injection gas ports 48. A valve piston 52 is biased closed by a gas charge dome 50 and a bellows assembly (i.e., convoluted bellows 56 in FIG. 2A or edge-welded bellows system 57 in FIG. 2B). At its distal end, the valve piston 52 moves relative to a valve seat 54 at the valve port 46 in response to pressure on the bellows 56 from the gas charge dome 50. A predetermined gas charge is applied to the dome 50 and bellows assembly (i.e., 56 or 57) biases the valve piston 52 against the valve seat 54 and close the valve port 46.
A check valve 58 in the gas-lift valves 40 is positioned downstream from the valve piston 52, valve seat 54, and valve port 46. The check valve 58 keeps flow from the production string (not shown) from going through the injection ports 48 and back into the casing (annulus) through the valve port 46. Yet, the check valve 58 allows injected gas from the valve port 46 to pass out the gas injection ports 48.
The bellows 56 on the valve 40a in FIG. 2A is a convoluted bellows. Although a spring-activated gas lift valve may be available for standard sizes and capable of higher pressures, such a bellows-activated gas lift valve 40a with a convoluted bellows is not available for standard sizes of 1″ and 1.5″, while being capable of operating pressures higher than 2000-2500 PSI range. Instead, existing gas lift valves 40a using convoluted bellows are rated to a maximum operating injection pressure of 2000-2500 PSI.
As a result, such a valve 40a is not capable of reaching high operating pressures. If exposed to higher pressures, the valve's convoluted bellows 56 would fail. For example, the bellows 56 may snake by forming a wave when exposed to high differential internal pressure, or the bellows 56 may split the convolutions by flattening when exposed to high external pressures. Finally, rapid pressure changes can contract and expand the bellows until the bellow's material fails due to fatigue.
Although a working pressure no higher than 2000-25000 PSI may be acceptable in some application, operators want to use gas lift system in higher working pressure of up to 5000-6000 PSI, for example. Unfortunately, high differential pressure across a bellows during operation reduces its cycle life. Therefore, existing gas lift valves and bellows are not designed to operate with set pressures or in operating pressures in excess of 2000 PSI without severe failure risks.
As one exception, the XLift gas lift valve available from Schlumberger has a bellows system for operating at high pressures. An example of this bellows system 57 is shown on the gas lift valve 40b of FIG. 2B. The edge-welded bellows system 57 is similar to that disclosed in U.S. Pat. No. 5,662,335. As shown, two sets 60a-b of dual bellows each include a seal bellows 62 and a counter bellows 64. The counter bellows 64 equalizes pressure exerted on the seal bellows 62 by delivering pressure of the injection gas to the oil in the system.
During operation, the valve piston 52 with its tungsten carbide ball on its distal end contacts the venturi seat 54, which acts as a positive stop for the gas lift valve 40b. None of the bellows 62, 64 of the bellows system 57 fully compresses. In the end, the arrangement of multiple bellows 62, 64 in the two sets 60a-b allow the gas lift valve to operate at higher pressures. Due to the requirements of the bellows system 57, however, the gas lift valve 40b must at least have a nominal size of 1.75-in. This requires the gas lift valve 40b to be used in a larger, custom designed gas lift mandrel, namely the XLG side pocket mandrel available from Schlumberger. Additionally, the complexity of the bellows system 57 has obvious disadvantages in the construction and operation of the gas lift valve 40b. 
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.